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Preparing Rubber Motors

There is a range of opinion and expertise regarding the preparation of rubber motors for free flight model airplanes from the professionalism of world championship competitors down to the relative ignorance (no offence intended) of the rank beginner. Somewhere in between are we (amateur) "experts" who have developed methods of preparation which satisfy our individual needs. We infest model airplane forums to dispense questionable wisdom to help answer perpetual novice questions from our knowledge hungry colleagues. By so doing, we spread our individual gospels throughout the hobby, invoking occasional disagreement as to best practice.

With this in mind, what follows is a system of rubber prep and management learned from others over 25 yrs of competitive vintage rubber powered free flight, that works for me.

Leave the rubber in its original sealed boxes and keep it in a dark and stable atmosphere of a cupboard in an unheated room. Don't use fridges/freezers simply because it's difficult to control humidity. Leave talc on the rubber until its time to make up a motor because it's so much easier to measure out as it slips through the fingers easily without clinging. Talc also takes up small amounts of moisture in the atmoshere particularly if the temperature drops unduly.

To make up a typical motor from (say) 1/4" strip, weigh out the total amount (eg; 100 grams) required and divide into two hanks as follows. For 16 and 12 strand motors - two equal parts, for 14 strand motors - 6/14ths and 8/14 ths. For 10 strand motors - 4/10 ths and 6/10 ths. Make up two separate loops using a favourite knot. Worth trying is a single half reef and bind the free ends tight with crochet cotton wrapped 5 or 6 times before knotting and trimming.

Fold the loop into the intended half motor, either 4, 6, or 8 stands and secure one end of the hank with a small rubber band to keep it tidy. Take both hanks to the sink, wash off the talc in warm soapy water (not detergent), knead the slimy bundle to remove all the talc, rinse in cold running water and allow it to drip off. When nearly dry, thoroughly lube with a favourite such as the excellent soft soap and glycerine mix, pulling, stretching and kneading, especially the knots. Bring the two hanks together at a bobbin and secure with a small band ready for cording.

Cord the motor as desired using a Tim Grey prop hook, securing 1 loop to each arm of the hook to stop the rubber climbing off the hook as each half tries to climb in opposition and bind with a small band. I favour 2 different cording methods. To determine the number of cording turns required, measure the length of motor in inches and multiply that number by 2.6. For freewheeling propellers, put half this number of cording turns on each half motor and bring the halves together at the Tim Grey hook as mentioned. Note, when the "halves" are unequal add (say) 5 turns to the thinner half and subtract 5 turns from the thicker half to equalise the tensions on each half. An alternative method, having determined the required cording turns as before, put half that number on each separate pair of strands, again bringing them to the Tim Grey hook, producing a loosely braided "rastafarian" motor ideal for folding propellers.

Wind the motor to 100 turns, stretch well, let it unwind to equalise the cording, pop it in a poly bag and seal. Keep the bagged motor in a dark place (usually) in the box with the model plus two other identical motors and the whole kit n' kaboodle is ready to go the field. When winding for flight, only go to maximum torque for the model (empirically determined at the trimming stage) and after the first flight return the motor to its poly bag. Use different motor for each of three (usually) qualifying flights and if lucky enough to get three maxes use the best of the three motors for the fly-off.

Back home inspect all three motors for damage, repair as required and return them to their bags and model box. All models (plus motors) are stored in a constant temperature north facing integral garage. Don't worry about keeping them super cool, just try to avoid too many atmospheric changes. The preserving effect of soap and glycerine allows motors to be kept, fully prepared for use for long periods of time. Motors go many months or even years between use and can be used in "balls out" competitions. They never seem to deteriorate, they rarely catastrophically break (except individual strands), unless careless with winding technique or lubrication, and because motors are used relatively infrequently, they alway give out full torque.

This process may suit only a small number of readers. The amateur "experts" already have their own system that works - so no need to change and the professionals may not even get to read it. However, those who are searching for their own system may want to consider if elements of this process might work for them. There is nothing to lose but time, so give it a try! More Tip n' Tricks?

There is a range of opinion and expertise regarding the preparation of rubber motors for free flight model airplanes from the professionalism of world championship competitors down to the relative ignorance (no offence intended) of the rank beginner. Somewhere in between are we (amateur) "experts" who have developed methods of preparation which satisfy our individual needs. We infest model airplane forums to dispense questionable wisdom to help answer perpetual novice questions from our knowledge hungry colleagues. By so doing, we spread our individual gospels throughout the hobby, invoking occasional disagreement as to best practice.

With this in mind, what follows is a system of rubber prep and management learned from others over 25 yrs of competitive vintage rubber powered free flight, that works for me.

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